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95-533: The building, a silver glass curtain wall skyscraper with 731,852 square feet (68,000 m) of floor space, includes retail and restaurant space, a conference room, a nine-story parking garage and a pedestrian bridge that links the lobby with 30th Street Station. The building's lighting, designed by Cline Bettridge Bernstein Lighting Design, includes a wall of LEDs on most of its facade that can change color to create various patterns and effects. The site of

190-419: A wind tunnel study is performed on large or unusually-shaped buildings. A scale model of the building and the surrounding vicinity is built and placed in a wind tunnel to determine the wind pressures acting on the structure in question. These studies take into account vortex shedding around corners and the effects of surrounding topography and buildings. Seismic loads in a curtain wall system are limited to

285-425: A 175,000 square feet (16,000 m ), 625 car parking garage. The pale-gray granite-clad skyscrapers feature setbacks on the north and south sides of the building, with the bottom floors containing 33,000 square feet (3,100 m ) and the upper floors 15,000 square feet (1,400 m ). The floors feature a large amount of floor space, a design influenced by IBM's needs in the 1980s. The two towers are topped with

380-416: A U-value of 0.2 or higher, which is equivalent to an R-value of 5 or lower. Infill refers to the large panels that are inserted into the curtain wall between mullions. Infills are typically glass but may be made up of nearly any exterior building element. Some common infills include metal panels, louvers, and photovoltaic panels. Infills are also referred to as spandrels or spandrel panels. Float glass

475-578: A building in which the outer walls are non-structural, instead serving to protect the interior of the building from the elements. Because the curtain wall façade carries no structural load beyond its own dead load weight, it can be made of lightweight materials. The wall transfers lateral wind loads upon it to the main building structure through connections at floors or columns of the building. Curtain walls may be designed as "systems" integrating frame, wall panel, and weatherproofing materials. Steel frames have largely given way to aluminum extrusions. Glass

570-632: A building to house its corporate headquarters . On March 30, 1990, after being sought after by numerous developers in Philadelphia and its suburbs, Conrail announced that it would be leasing 27 floors of Two Commerce Square. With a lead tenant secured, construction of the identical tower commenced in July 1990. Two Commerce Square was completed in July 1992 and Conrail began moving in approximately 3,000 employees in September of that year. Two Commerce Square marked

665-504: A combination of both. Their exterior walls were load-bearing , supporting much or all of the load of the entire structure. The nature of the materials resulted in inherent limits to a building's height and the maximum size of window openings. The development and widespread use of structural steel and later reinforced concrete allowed relatively small columns to support large loads. The exterior walls could be non-load bearing, and thus much lighter and more open than load-bearing walls of

760-404: A curtain wall. Water penetration is defined as water passing from the exterior of the building to the interior of the curtain wall system. Sometimes, depending on the building specifications , a small amount of controlled water on the interior is deemed acceptable. Controlled water penetration is defined as water that penetrates beyond the inner most vertical plane of the test specimen, but has

855-426: A designed means of drainage back to the exterior. AAMA Voluntary Specifications allow for controlled water penetration while the underlying ASTM E1105 test method would define such water penetration as a failure. To test the ability of a curtain wall to withstand water penetration in the field, an ASTM E1105 water spray rack system is placed on the exterior side of the test specimen, and a positive air pressure difference

950-403: A given curtain wall is anchored at 12-foot (144 in) floor heights. The allowable deflection would then be 144/175 = 0.823 inches, which means the wall is allowed to deflect inward or outward a maximum of 0.823 inches at the maximum wind pressure. However, some panels require stricter movement restrictions, or certainly those that prohibit a torque-like motion. Deflection in mullions

1045-581: A glass office skyscraper next to 30th Street Station. Called the Cira Centre, the skyscraper would be designed by architect César Pelli . The plan also included replacing the rest of the parking deck with a landscaped entrance plaza and parking lot. The plan to develop the land around 30th Street Station was part of a nationwide effort by Amtrak , which owns the land and the train station, to earn revenue from its real estate holdings. Amtrak's effort also emphasizes projects that would increase ridership. Also part of

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1140-422: A high heat transfer coefficient, meaning that aluminum is a very good conductor of heat. This translates into high heat loss through aluminum (or steel) curtain wall mullions. There are several ways to compensate for this heat loss, the most common way being the addition of thermal breaks . These are barriers between exterior metal and interior metal, usually made of polyvinyl chloride (PVC). These breaks provide

1235-515: A joint venture between Maguire Thomas Partners and IBM . IBM leased more than half of One Commerce Square for the company's Mid-Atlantic headquarters. Construction of the first phase, which included One Commerce Square, the plaza, and retail space, began in 1985 and was completed in 1987. The project's second phase, Two Commerce Square, did not begin until a lead tenant was secured for the building in 1990. Consolidated Rail Corporation (Conrail) agreed to be Two Commerce Square's lead tenant and make

1330-519: A musical group called String Theory whose performance in the Cira Centre's lobby included a large harp and 12 100 feet (30 m) long brass wires attached to the building. The Cira Centre was the first office skyscraper to be completed in Philadelphia since Two Commerce Square in 1992. On August 31, 2007, the University of Pennsylvania and Brandywine Realty Trust announced their plans to build Cira Centre South . Located south of 30th Street Station and

1425-466: A pair of standing stone diamonds with cutout squares in the center. The towers are separated by a 30,000 square feet (2,800 m ) paved courtyard. Tables and chairs are arranged around a large pink granite circular fountain in the plaza's center. The plaza was designed by Laurie Olin of Hanna/Olin Ltd. Impressed by Commerce Square's plaza, Philadelphia's city planning commission included influences from

1520-407: A shop, but installation and glazing is typically performed at the jobsite. Very similar to a stick system, a ladder system has mullions which can be split and then either snapped or screwed together consisting of a half box and plate. This allows sections of curtain wall to be fabricated in a shop, effectively reducing the time spent installing the system onsite. The drawbacks of using such a system

1615-403: A significant decrease in the thermal conductivity of the curtain wall. However, since the thermal break interrupts the aluminum mullion, the overall moment of inertia of the mullion is reduced and must be accounted for in the structural analysis and deflection analysis of the system. Thermal conductivity of the curtain wall system is important because of heat loss through the wall, which affects

1710-477: A thin plastic interlayer; copper wall cladding , and panels consisting of metal sheets bonded to rigid insulation, with or without an inner metal sheet to create a sandwich panel. Other opaque panel materials include fiber-reinforced plastic (FRP) and terracotta . Terracotta curtain wall panels were first used in Europe, but only a few manufacturers produce high quality modern terracotta curtain wall panels. A louver

1805-407: A wall is quite noticeable, public perception may raise undue concern that the wall is not strong enough. Deflection limits are typically expressed as the distance between anchor points divided by a constant number. A deflection limit of L/175 is common in curtain wall specifications, based on experience with deflection limits that are unlikely to cause damage to the glass held by the mullion. Say that

1900-469: A wall of light using LEDs . The 26W RGB LED fixtures are hidden in shadow boxes behind the glass curtain wall and are obscured during the day by the building's reflective glass. The LED lights are able to change color to create different patterns and effects on the building's facade. Designs used on the building include a large "P" for the Philadelphia Phillies , the infamous bald eagle head logo for

1995-403: Is transparent , translucent , or opaque, or in varying degrees thereof. Transparent glass usually refers to vision glass in a curtain wall. Spandrel or vision glass may also contain translucent glass, which could be for security or aesthetic purposes. Opaque glass is used in areas to hide a column or spandrel beam or shear wall behind the curtain wall. Another method of hiding spandrel areas

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2090-406: Is 27,300 square feet (2,500 m) and the floors feature 9 feet (2.7 m) ceilings and 360-degree panoramic views. Building amenities include fourteen high speed and two freight elevators, a health club, restaurants and retail space and a conference center. A pedestrian bridge designed by BLT Architects crosses Arch Street linking the Cira Centre with 30th Street Station . The bridge connects

2185-404: Is a normal force acting on the building as the result of wind blowing on the building. Wind pressure is resisted by the curtain wall system since it envelops and protects the building. Wind loads vary greatly throughout the world, with the largest wind loads being near the coast in hurricane -prone regions. For each project location, building codes specify the required design wind loads. Often,

2280-403: Is a separate criterion in curtain wall design and analysis . This often affects the selection of materials and sizes for design of the system. The allowable bending strength for certain aluminum alloys, such as those typically used in curtain wall framing, approaches the allowable bending strength of steel alloys used in building construction. Relative to other building components, aluminum has

2375-418: Is accounted for by cutting horizontal mullions slightly short and allowing a space between the horizontal and vertical mullions. In unitized curtain wall, a gap is left between units, which is sealed from air and water penetration by gaskets. Vertically, anchors carrying wind load only (not dead load) are slotted to account for movement. Incidentally, this slot also accounts for live load deflection and creep in

2470-440: Is applied to the system. This set up simulates a wind driven rain event on the curtain wall to check for field performance of the product and of the installation. Field quality control and assurance checks for water penetration has become the norm as builders and installers apply such quality programs to help reduce the number of water damage litigation suits against their work. One of the disadvantages of using aluminum for mullions

2565-406: Is beautifully demonstrated by his design for the lobby level, including the splendid garden, of Commerce Square at 20th and Market streets, which I think will prove to be one of the finest commercial projects to be built in this century." One Commerce Square's main tenant is IBM, which moved into the skyscraper when it opened in 1987. IBM initially occupied nearly half of One Commerce Square, but in

2660-409: Is by far the most common curtain wall glazing type. It can be manufactured in an almost infinite combination of color, thickness, and opacity . For commercial construction, the two most common thicknesses are 1 ⁄ 4 inch (6.4 mm) monolithic and 1 inch (25 mm) insulating glass . 1/4 inch glass is typically used only in spandrel areas, while insulating glass is used for the rest of

2755-427: Is controlled by different shapes and depths of curtain wall members. The depth of a given curtain wall system is usually controlled by the area moment of inertia required to keep deflection limits under the specification. Another way to limit deflections in a given section is to add steel reinforcement to the inside tube of the mullion. Since steel deflects at one-third the rate of aluminum, the steel will resist much of

2850-408: Is defined as the weight of structural elements and the permanent features on the structure. In the case of curtain walls, this load is made up of the weight of the mullions, anchors and other structural components of the curtain wall, as well as the weight of the infill material. Additional dead loads imposed on the curtain wall may include sunshades or signage attached to the curtain wall. Wind load

2945-478: Is now common. In Scandinavia, the first curtain walls with quadruple-pane have been built. Larger thicknesses are typically employed for buildings or areas with higher thermal, relative humidity , or sound transmission requirements, such as laboratory areas or recording studios . In residential construction, thicknesses commonly used are 1 ⁄ 8 inch (3.2 mm) monolithic and 5 ⁄ 8 inch (16 mm) insulating glass. Glass may be used which

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3040-403: Is provided in an area where mechanical equipment located inside the building requires ventilation or fresh air to operate. They can also serve as a means of allowing outside air to filter into the building to take advantage of favorable climatic conditions and minimize the usage of energy-consuming HVAC systems. Curtain wall systems can be adapted to accept most types of louver systems to maintain

3135-598: Is reduced structural performance and visible joint lines down the length of each mullion. Unitized curtain walls entail factory fabrication and assembly of panels and may include factory glazing. These completed units are installed on the building structure to form the building enclosure. Unitized curtain wall has the advantages of: speed; lower field installation costs; and quality control within an interior climate-controlled environment. The economic benefits are typically realized on large projects or in areas of high field labor rates. A common feature in curtain wall technology,

3230-455: Is that its modulus of elasticity is about one-third that of steel. This translates to three times more deflection in an aluminum mullion compared to a similar steel section under a given load. Building specifications set deflection limits for perpendicular (wind-induced) and in-plane (dead load-induced) deflections. These deflection limits are not imposed due to strength capacities of the mullions. Rather, they are designed to limit deflection of

3325-519: Is the 1988 First Interstate Tower fire in Los Angeles, California . The fire leapfrogged up the tower by shattering the glass and then consuming the aluminum framing holding the glass. Aluminum's melting temperature is 660 °C, whereas building fires can reach 1,100 °C. The melting point of aluminum is typically reached within minutes of the start of a fire. Fireman knock-out glazing panels are often required for venting and emergency access from

3420-469: Is the air which passes through the curtain wall from the exterior to the interior of the building. The air is infiltrated through the gaskets, through imperfect joinery between the horizontal and vertical mullions, through weep holes , and through imperfect sealing. The American Architectural Manufacturers Association (AAMA) is an industry trade group in the U.S. that has developed voluntary specifications regarding acceptable levels of air infiltration through

3515-424: Is through shadow box construction (providing a dark enclosed space behind the transparent or translucent glass). Shadow box construction creates a perception of depth behind the glass that is sometimes desired. Thin blocks (3 to 4 inches (76 to 102 millimetres)) of stone can be inset within a curtain wall system. The type of stone used is limited only by the strength of the stone and the ability to manufacture it in

3610-806: Is typically used for infill because it can reduce construction costs, provide an architecturally pleasing look, and allow natural light to penetrate deeper within the building. However, glass also makes the effects of light on visual comfort and solar heat gain in a building more difficult to control. Other common infills include stone veneer , metal panels, louvres , and operable windows or vents. Unlike storefront systems, curtain wall systems are designed to span multiple floors, taking into consideration building sway and movement and design requirements such as thermal expansion and contraction; seismic requirements; water diversion; and thermal efficiency for cost-effective heating, cooling, and interior lighting. Historically, buildings were constructed of timber, masonry, or

3705-406: The perimeter slab edge , which is a gap between the floor and the curtain wall, is essential to slow the passage of fire and combustion gases between floors. Spandrel areas must have non-combustible insulation at the interior face of the curtain wall. Some building codes require the mullion to be wrapped in heat-retarding insulation near the ceiling to prevent the mullions from melting and spreading

3800-495: The Philadelphia Eagles , and images of falling snowflakes during the winter season. White 0.12W LED lights are also used in the lobby and building's elevators. In the lobby, the white LEDs are mounted on the 50 feet (15 m) tall wall that separates the lobby from the neighboring parking garage. The Philadelphia Inquirer 's architecture critic Inga Saffron called the Cira Centre "a gorgeous object". She praised how

3895-413: The rainscreen principle theorizes that equilibrium of air pressure between the outside and inside of the "rainscreen" prevents water penetration into the building. For example, the glass is captured between an inner and an outer gasket in a space called the glazing rebate. The glazing rebate is ventilated to the exterior so that the pressure on the inner and outer sides of the outer gasket is the same. When

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3990-644: The American Southwest and in the Mideast for avoiding dust, as well as avoiding soot and smoke staining in polluted urban areas. Commerce Square Commerce Square is a Class-A, high-rise office building complex in Center City Pennsylvania . Commerce Square consists of One and Two Commerce Square, two identical 41- story office towers 565 feet (172 m) high that surround a paved courtyard of 30,000 square feet (2,800 m ). Architecturally,

4085-469: The Cira Centre used to be a parking deck that sat over rail tracks across Arch Street from 30th Street Station in West Philadelphia . Plans to develop the rail yards north and northwest of 30th Street Station had been around for decades. Among the proposed ideas for the rail yards included building a new city hall and, in the 1960s before Veterans Stadium was built, a sports stadium was proposed for

4180-544: The Cira Centre's lobby with the SEPTA regional rail section. The location right next to 30th Street Station allows direct access to the Northeast Corridor , SEPTA's regional rail , and Philadelphia International Airport . The lighting design was done by Cline Bettridge Bernstein Lighting Design. Cira Centre's architects did not want any light fixtures protruding from the building so Cline Bettridge Bernstein decided to create

4275-474: The Cira Centre, Brandywine Realty Trust could now proceed with construction of the skyscraper. Turner Construction was awarded $ 116 million contract to build the Cira Centre in February 2004 and construction began later that year. The building was topped off November 16, 2004. The topping off ceremony, the first in Philadelphia since 1999, was attended by numerous dignitaries including Mayor John Street . The beam

4370-473: The Cira Centre, the new project is designed by the same architecture firm as the Cira Centre. Cira Centre South will include a 40–50 story office tower and a 25–30 story residential tower. The project also includes a parking garage and conversion of the U.S. Postal Service building on 30th and Market Streets into offices for the Internal Revenue Service . The parking garage and Post Office conversion

4465-528: The Consolidated Rail Corporation made 728,000 square feet (68,000 m ) of the tower its corporate headquarters. Since being bought by Norfolk Southern and CSX Transportation, Conrail and CSX now share about 5,000 square feet (460 m ) in the tower. Today Two Commerce Square has become a center of accounting and consulting firms, the largest of which is PricewaterhouseCoopers , which occupies 215,000 square feet (20,000 m ). Occupying

4560-439: The U.S. and all U.S. embassies built on foreign soil must have some provision for resistance to bomb blasts. Since the curtain wall is at the exterior of the building, it becomes the first line of defense in a bomb attack. As such, blast resistant curtain walls are designed to withstand such forces without compromising the interior of the building to protect its occupants. Since blast loads are very high loads with short durations,

4655-443: The architectural firm IM Pei & Partners (now called Pei Cobb Freed & Partners ) to design the complex. Using a design by a leading architectural firm as incentive, Maguire approached IBM , a company he had past associations with. By early November 1984, after negotiations with Maguire, IBM agreed to be a joint partner in the development. IBM also agreed to serve as the lead tenant for One Commerce Square, occupying about half

4750-532: The area. In 1970, Philadelphia considered holding a bicentennial exposition over the rail yards, and the area was also considered for the Pennsylvania Convention Center . In 1985 an office, hotel and shopping complex was proposed by real estate developer Gerald D. Hines , and in 1992 an idea for a stadium was again proposed for the site. Nothing ever came out of the plans. On May 8, 2002, Brandywine Realty Trust announced its intentions to build

4845-431: The building (sometimes spandrel glass is specified as insulating glass as well). The 1 inch insulation glass is typically made up of two 1/4-inch lites of glass with a 1 ⁄ 2 inch (13 mm) airspace. The air inside is usually atmospheric air, but some inert gases , such as argon or krypton , may be used in order to offer better thermal transmittance values. In Europe, triple-pane insulating glass infill

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4940-542: The building as its headquarters for the Mid-Atlantic region . Commerce Square would be split between two buildings, One Commerce Square being built first, and the second tower, Two Commerce Square, being built later once a lead tenant was secured. Plans for Commerce Square were officially announced on November 16, 1984 at a press conference held by Maguire and IBM at the Bellevue-Stratford Hotel . The first phase of

5035-457: The building blocks of structural understanding were laid for the development of curtain walls. Oriel Chambers (1864) and 16 Cook Street (1866), both built in Liverpool , England , by local architect and civil engineer Peter Ellis , are characterised by their extensive use of glass in their facades. Toward the courtyards they boasted metal-framed glass curtain walls, which makes them two of

5130-455: The building changes shape when viewing it from different angles, describing the building as a "shape-shifter". She also praised the glass façade, which she felt "helps marry the delicate modern tower with the weighty, neoclassical train station". Saffron was critical that when "viewed straight on from the south side, the Cira becomes just another staid corporate glass tower". She was also critical of how

5225-465: The city. Though IBM had initially occupied nearly half of One Commerce Square, by 1993 it was using only one-fifth of the building. In 1996, Maguire Thomas Partners split up, leaving the ownership of Commerce Square to Thomas Properties Group Inc. alone. After the split, Thomas Properties renegotiated mortgage financing of the Commerce Square towers. Thomas Properties Group successfully renegotiated

5320-447: The company still had concerns about filling the space soon to be vacated by Conrail. In October 1996 Conrail was bought by Norfolk Southern Railway and CSX Transportation . The merger was concluded in May 1998 and the former Conrail offices and employees began to be moved out of the building. In the merger deal, CSX Transportation absorbed Conrail's 15-year lease. CSX was responsible for paying

5415-413: The completion of the compartment (or envelope). The use of fire sprinklers has been shown to mitigate this matter. As such, unless the building is sprinklered , fire may still travel up the curtain wall, if the glass on the exposed floor is shattered from heat, causing flames to lick up the outside of the building. Falling glass can endanger pedestrians, firefighters and firehoses below. An example of this

5510-556: The complex in a new building code governing open space. Commerce Square was praised for its design of two towers surrounding a plaza. The Philadelphia Inquirer said "Its most positive aspect is that it avoids the developers' cliches of atriums and shopping malls and makes a real urban place. It expresses great confidence in Philadelphia, and even more important, in the whole idea of living in cities." Renowned Philadelphia urban planner Edmund N. Bacon praised Commerce Square and its plaza by saying "[Olin's] sensitivity for urban design

5605-595: The curtain wall at 900–910 Lake Shore Drive, where the curtain is an autonomous aluminum and glass skin. After 900–910, Mies's curtain wall appeared on all of his subsequent high-rise building designs, including the Seagram Building in New York. The widespread use of aluminium extrusions for mullions began during the 1970s. Aluminum alloys offer the unique advantage of being able to be easily extruded into nearly any shape required for design and aesthetic purposes. Today,

5700-398: The curtain wall response should be analyzed in a dynamic load analysis, with full-scale mock-up testing performed prior to design completion and installation. Blast resistant glazing consists of laminated glass , which is meant to break but not separate from the mullions. Similar technology is used in hurricane-prone areas for impact protection from wind-borne debris. Air infiltration

5795-493: The debt for Two Commerce Square with Bank of America , but was unable to renegotiate the debt with One Commerce Square's prime mortgage holder, Mitsubishi Trust and Banking Corporation . To break the deadlock, Philadelphia Plaza Associates filed for Chapter 11 bankruptcy protection . Thomas Properties Group was then the parent company of Philadelphia Plaza Associates which owned Commerce Square. Philadelphia Plaza Associates emerged from bankruptcy reorganization early in 1998, but

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5890-533: The decades since, consolidation has reduced the company's presence in the building. Other tenants in One Commerce Square include Ernst & Young LLP , Stradley Ronon Stevens & Young LLP, The Pew Charitable Trusts , Fiserv Securities Inc., Thorp Reed & Armstrong LLP, and Delaware Investments , which also leases office space in Two Commerce Square. When Two Commerce Square opened in 1992,

5985-609: The design complexity and shapes available are nearly limitless. Custom shapes can be designed and manufactured with relative ease. The Omni San Diego Hotel curtain wall in California, designed by architectural firm Hornberger and Worstel and developed by JMI Realty, is an example of a unitized curtain-wall system with integrated sunshades. The vast majority of ground-floor curtain walls are installed as long pieces (referred to as sticks ) between floors vertically and between vertical members horizontally. Framing members may be fabricated in

6080-499: The design team and designed Cira Centre's core and neighboring parking garage. The building was designed to be seen from all sides with the northwest and southeast corners removed giving the Cira Centre a different shape when viewed from different directions. The building's 731,852 square feet (68,000 m) includes 690,000 square feet (64,000 m) of office space and 37,000 square feet (3,400 m) of conference, retail space and related amenities space. The average floor-plate size

6175-529: The end of the skyscraper boom of the 1980s, being the last office skyscraper to be built in Philadelphia until the Cira Centre in 2005. After the office-building boom of the 1980s, the 1990s saw an office glut that resulted in numerous vacancies and reduced leasing rates throughout Center City. In 1993 IBM, struggling financially, was shrinking its workforce and consolidating its operations nationwide, and its plans included moving some of its local employees out of

6270-617: The exterior. Knock-out panels are generally fully tempered glass to allow full fracturing of the panel into small pieces and relatively safe removal from the opening. Curtain walls and perimeter sealants require maintenance to maximize service life. Perimeter sealants, properly designed and installed, have a typical service life of 10 to 15 years. Removal and replacement of perimeter sealants require meticulous surface preparation and proper detailing. Aluminum frames are generally painted or anodized . Care must be taken when cleaning areas around anodized material as some cleaning agents will destroy

6365-601: The finest commercial projects to be built in this century". Commerce Square was part of an office-building boom that took place in the late 1980s in Philadelphia , Pennsylvania . During the boom numerous skyscrapers were constructed in the West Market Street neighborhood of Center City . The US$ 300 million development of Commerce Square was led by Robert F. Maguire III, co-managing partner of Maguire Thomas Partners of Los Angeles. To get his project moving, Maguire engaged

6460-815: The finish. Factory applied fluoropolymer thermoset coatings have good resistance to environmental degradation and require only periodic cleaning. Recoating with an air-dry fluoropolymer coating is possible but requires special surface preparation and is not as durable as the baked-on original coating. Anodized aluminum frames cannot be "re-anodized" in place but can be cleaned and protected by proprietary clear coatings to improve appearance and durability. Stainless steel curtain walls require no coatings, and embossed, as opposed to abrasively finished, surfaces maintain their original appearance indefinitely without cleaning or other maintenance. Some specially textured matte stainless steel surface finishes are hydrophobic and resist airborne and rain-borne pollutants. This has been valuable in

6555-451: The fire to the floor above. The firestop at the perimeter slab edge is considered a continuation of the fire-resistance rating of the floor slab. The curtain wall itself, however, is not ordinarily required to have a rating. This causes a quandary as compartmentalization (fire protection) is typically based upon closed compartments to avoid fire and smoke migrations beyond each engaged compartment. A curtain wall by its very nature prevents

6650-447: The first curtain walls were made with steel mullions , and the polished plate glass was attached to the mullions with asbestos- or fiberglass-modified glazing compound. Eventually silicone sealants or glazing tape were substituted for the glazing compound. Some designs included an outer cap to hold the glass in place and to protect the integrity of the seals. The landmarks of curtain wall design as it came to dominate construction were

6745-523: The floor slabs of the building structure. Accidental explosions and terrorist threats have brought on increased concern for the fragility of a curtain wall system in relation to blast loads. The bombing of the Alfred P. Murrah Federal Building in Oklahoma City, Oklahoma, has spawned much of the current research and mandates in regards to building response to blast loads. Currently, all new federal buildings in

6840-415: The glass (which may break under excessive deflection), and to ensure that the glass does not come out of its pocket in the mullion. Deflection limits are also necessary to control movement at the interior of the curtain wall. Building construction may be such that there is a wall located near the mullion, and excessive deflection can cause the mullion to contact the wall and cause damage. Also, if deflection of

6935-403: The granite-clad towers feature setbacks on the north and south sides of the building and are topped with a pair of stone diamonds with cutout squares in the center. The towers were built as part an office-building boom Philadelphia was experiencing on West Market Street in the late 1980s. Designed by IM Pei & Partners (now called Pei Cobb Freed & Partners ), the towers were developed in

7030-688: The heating and cooling costs of the building. On a poorly performing curtain wall, condensation may form on the interior of the mullions. This could cause damage to adjacent interior trim and walls. Rigid insulation is provided in spandrel areas to provide a higher R-value at these locations. Thermally-broken mullions with double- or triple-glazed IGUs are often referred to as "high-performance" curtain walls. While these curtain wall systems are more energy-efficient than older, single-glazed versions, they are still significantly less efficient than opaque (solid) wall construction. For example, nearly all curtain wall systems, thermally-broken or otherwise, have

7125-573: The interstory drift induced on the building during an earthquake . In most situations, the curtain wall is able to naturally withstand seismic and wind induced building sway because of the space provided between the glazing infill and the mullion. In tests, standard curtain wall systems are typically able to withstand up to three inches (76 mm) of relative floor movement without glass breakage or water leakage. Snow loads and live loads are not typically an issue in curtain walls, since curtain walls are designed to be vertical or slightly inclined. If

7220-841: The lease, but the 728,000 square feet (68,000 m ) of space was subleased, offsetting the cost. Between 1999 and 2000, as Conrail offices were phased out of Two Commerce Square, Thomas Properties filled the newly vacated space with new tenants. Located on West Market Street in Center City Philadelphia , Commerce Square comprises twin 41- story 565 feet (172 m) office towers designed by Henry N. Cobb and Douglas Gardner of IM Pei & Partners. Commerce Square covers an entire block, between 20th and 21st Streets and Market Street and John F. Kennedy Boulevard . Commerce Square contains 2,200,000 square feet (200,000 m ), which includes 1,850,000 square feet (170,000 m ) of office space, 92,000 square feet (8,500 m ) lobby, and

7315-459: The load at a lower cost or smaller depth. Deflection in curtain wall mullions also differs from deflection of the building structure, whether concrete, steel, or timber. Curtain wall anchors must be designed to allow differential movement between the building structure and the curtain wall. Strength (or maximum usable stress ) available to a particular material is not related to its material stiffness (the material property governing deflection); it

7410-582: The past. This gave way to increased use of glass as an exterior façade, and the modern-day curtain wall was born. Post-and-beam and balloon framed timber structures effectively had an early version of curtain walls, for their frames supported loads that allowed the walls themselves to serve other functions, such as keeping weather out and allowing light in. When iron began to be used extensively in buildings in late 18th-century Britain, such as at Ditherington Flax Mill , and later when buildings of wrought iron and glass such as The Crystal Palace were built,

7505-407: The pressure is equal across this gasket, water cannot be drawn through joints or defects in the gasket. A curtain wall system must be designed to handle all loads imposed on it as well as keep air and water from penetrating the building envelope. The loads imposed on the curtain wall are transferred to the building structure through the anchors which attach the mullions to the building. Dead load

7600-599: The project included One Commerce Square, retail and restaurant space, a plaza , and an underground parking garage. Construction began with the first phase on June 10, 1985. One Commerce Square was topped off with a ceremony on June 6, 1986, and the skyscraper officially opened on October 23, 1987. In 1987 the Consolidated Rail Corporation (Conrail) indicated it wanted to consolidate its offices spread out across Philadelphia into one office building. In May 1988, Conrail solicited proposals from developers for

7695-446: The project was construction of a parking garage. The nine- story , 1,525 car garage is intended to alleviate a parking shortage at 30th Street Station. Planned since 1996, the $ 50 million parking garage began construction in 2003 and was opened in May 2004. The site where Cira Centre sits, was once designated a Keystone Opportunity Improvement Zone (KOZ). The KOZ was designed to encourage development in poor and blighted areas by exempting

7790-414: The proper shape and size. Common stone types used are: calcium silicate , granite , marble , travertine , limestone , and engineered stone . To reduce weight and improve strength, the natural stone may be attached to an aluminum honeycomb backing. Metal panels can take various forms including stainless steel, aluminum plate; aluminum composite panels consisting of two thin aluminum sheets sandwiching

7885-427: The same architectural sightlines and style while providing desired functionality. Most curtain wall glazing is fixed, meaning that there is no access to the exterior of the building except through doors. However, windows or vents can be glazed into the curtain wall system as well, to provide required ventilation or operable windows. Nearly any window type can be made to fit into a curtain wall system. Firestopping at

7980-414: The skyscraper its corporate headquarters after a two-year search for office space in the region. Two Commerce Square ended the skyscraper construction boom of the 1980s when it was completed in 1992. No other office skyscraper was built in Philadelphia until Brandywine Realty Trust (NYSE: BDN) built the Cira Centre in 2005. In the 1990s, Commerce Square's lead tenants reduced their presence dramatically in

8075-413: The slope of a wall exceeds 20 degrees or so, these loads may need to be considered. Thermal loads are induced in a curtain wall system because aluminum has a relatively high coefficient of thermal expansion . This means that over the span of a couple of floors, the curtain wall will expand and contract some distance, relative to its length and the temperature differential. This expansion and contraction

8170-411: The surrounding railroad tracks and highways isolated the building. Tenants of the Cira Centre include BlackRock , Dechert LLP, Baker Hostetler LLP, Reger Rizzo & Darnall, LLP, Attalus Capital, SCA , LLR Partners, Lubert Adler, Iron Stone Real Estate Partners , Capsicum LLC, CYTO PHL, and McKinsey & Company . Curtain wall (architecture) A curtain wall is an exterior covering of

8265-495: The tenants of the building from almost all state and local taxes. On December 24, 2003 Brandywine Realty Trust announced the first tenants to lease room in the Cira Centre. Brandywine Realty Trust signed leases with Dechert LLP , Woodcock Washburn LLP, and Attalus Capital. Dechert LLP and Woodcock Washburn LLP were moving from other city skyscrapers, the Bell Atlantic Tower and One Liberty Place respectively. Attalus Capital

8360-412: The tower since its 1992 opening, professional services firm Ernst & Young LLP leased 115,000 square feet (11,000 m ) of the tower until relocating to One Commerce Square in early 2012. Other related firms include Delaware Investments which leases 125,000 square feet (12,000 m ) and Grant Thornton LLP . Other tenants also fill the tower, these include Leaf Financial Corporation, which leases

8455-480: The towers. IBM moved some of its operations out of Philadelphia in the early 1990s, and Conrail was bought by Norfolk Southern Railway and CSX Transportation later in the decade. Almost all of Conrail's operations were moved out of Philadelphia by the 2000s. Commerce Square was praised mainly for its design of two towers surrounding a plaza. Renowned Philadelphia urban planner Edmund N. Bacon praised Commerce Square and its plaza by saying it "will prove to be one of

8550-561: The very different systems used by the United Nations Headquarters and the Lever House completed in 1952. Ludwig Mies van der Rohe 's curtain wall is one of the most important aspects of his architectural design. Mies first began prototyping the curtain wall in his high-rise residential building designs along Chicago's lakeshore, achieving the look of a curtain wall at 860-880 Lake Shore Drive Apartments . He finally perfected

8645-500: The world's first buildings to include this architectural feature. Oriel Chambers is listed in the Guinness Book of Records as the earliest such building. The extensive glass walls allowed light to penetrate further into the building, utilizing more floor space and reducing lighting costs. Oriel Chambers comprises 43,000 sq ft (4,000 m ) set over five floors without an elevator , which had only recently been invented and

8740-464: Was completed in 2010. Evo, the residential tower, was completed in 2014. The FMC tower was completed in 2016. The Cira Centre is a 29-story, 437-foot (133 m) silver glass curtain wall skyscraper. The skyscraper sits next to 30th Street Station in the University City neighborhood of Philadelphia . The US$ 180 million Cira Centre was designed by architect Cesar Pelli. BLT Architects coordinated

8835-517: Was moving its offices from Bala Cynwyd, Pennsylvania . Dechert and Woodcock Washburn moving to the Cira Centre fueled the KOZ controversy because Dechert and Woodcock Washburn were wealthy law firms and would no longer have to pay taxes for numerous years. On December 31, 2018, Cira Centre's KOZ designation had expired, since it is not to exceed 15 years. By 2006, about 60 percent of Cira Centre's tenants came from within Philadelphia. Having secured tenants for

8930-534: Was not yet widespread. The Statue of Liberty (1886) features a thin, non-load-bearing copper skin. Extensive use of glass became required for large factory buildings to allow light for manufacture, sometimes making it seem like they had all glass facades. An early example of an all-steel curtain wall used in the classical style is the Kaufhaus Tietz  [ de ] department store on Leipziger Straße, Berlin , built in 1901 (since demolished). Some of

9025-446: Was raised shortly before 1:00 PM and was signed by workers and guests. The Cira Centre's glass facade was completely in place by the end of July 2005. The Cira Centre opened on October 31, 2005 with 93 percent of the building leased. Dechert was the first company to move employees into the building with many of rest of the tenants not moving in until early 2006. Cira Centre held its grand opening on December 1. The grand opening featured

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